The present invention relates generally to the field of testing valves, and more specifically, to the field of non-intrusively testing of check valves.
Valves have been used for years to control the flow and pressure of fluids through conduits. A check valve is a type of one-way, self-actuating valve used to permit fluid flow in only one direction. A check valve normally includes a check valve disk located within a check valve chamber and movable between a backstop and a seat. As fluid flows in the allowed direction, the valve is opened by the force of the flowing fluid. However, as the fluid stops flowing or attempts to reverse and flow in the opposite direction, a properly operating check valve closes. Several common types of check valves include swing check, piston lift, ball, stop check, and duo check.
Check valves are often used in environments where a reversal of flow would be very damaging or dangerous. Failures of check valves have even been known to produce the extremely harmful rises in pressure known as water hammers. Because all of the elements of a check valve are normally located inside the valve chamber, the condition of a check valve is very difficult to monitor. Potentially hazardous conditions may go undetected for extended periods of time. To test a check valve, an operator normally must disassemble the valve to verify operability and inspect each element for degradation and wear to predict future operability. This process is very time consuming and costly. Furthermore, the operator may unknowingly fail to properly reconstruct the valve after inspection, thus creating additional, undetected problems.
Ideally, while fluid flows through a check valve, the check valve disk remains firmly positioned against the backstop of the check valve, thus reducing wear and degradation of the check valve elements. However, it is well-known in the industry that undersized valves, oversized valves, and turbulent conditions in the fluid can result in the check valve disk moving from this position. These conditions often lead to continual damaging impacts between the check valve disk and the backstop or the seat. They also contribute to the check valve disk "fluttering" back and forth in the fluid which also tends to degrade the check valve. Before the invention of the method and apparatus of U.S. Pat. No. 4,977,778, from which this invention claims priority, there were not practical methods in the prior art to non-intrusively check for these harmful movements.